Cancer cells are characterized by a strong tendency toward massive proliferation, often at the expense of normal cells. Control mechanisms triggered by membrane-membrane interactions between cells as the cell density increases are bypassed. One of the more promising techniques for studying membrane phenomena is that of spin-labeling. A reporter molecule similar in structure to the naturally occurring phospholipids through containing a paramagnetic nitroxide group is diffused into the membrane. Important information about the local environment of the probe within the biological mebrane can be secured from an analysis of the electron spin resonance spectra of the nitroxide reporter group. In continuing our previous work with new nitroxide spin-labels we intend to determine the polar headgroup and fatty acid side chain specificity in the lipid-protein and lipid-lipid interactions in the membranous cytochrome oxidase system using techniques and methods of analysis already in use at the University of Oregon. Central to this effort is the synthesis of several new well-defined spin-labeled phospholipids containing polar headgroups other than choline.